The overall goal of the proposed studies is to elucidate the mechanisms of thyrotropin (TSH)-receptor interaction and propagation of biological signal and to determine the structure of TSH receptor in normal human thyroid and thyroid tumors. TSH radio-receptor assay will be used to quantitate the levels and binding parameters of specific 125I-TSH binding to human thyroid particulate and solubilized plasma membrane components. Factors influencing specific binding such as assay conditions and composition, purity of receptor preparations, ionic environment, competing agents and putative receptor-specific agents (gangliosides and anti-receptor antibodies) will be investigated to distinguish the physiological receptor from others of low affinity. The role of cooperative site-site interactions and binding compartmentalization will be evaluated from intrinsic kinetic parameters obtained by equilibrium saturation analysis complemented by analysis of the time/temperature dependency of receptor-hormone association/dissociation as a function of receptor occupancy. Expression of receptor function by adenylate cyclase and protein kinase activation will be investigated as monitors of biological activity and as markers to identify those macromolecular elements involved in TSH action during receptor solubilization. The characteristics of solubilized TSH receptors will be studied using an affinity-labeling method and after receptor purification by affinity chromatography. Concomittant studies on selected thyroid tumors may permit identification of components which may be abnormal or absent when compared to normal tissue.